Read the 'magic' portion of 'struct blk_io_trace' first when reading the
tracefile and only if all magic checks succeed, read the rest of the
trace.

This is a preparation of supporting multiple trace protocol versions.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 blkparse.c | 44 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/blkparse.c b/blkparse.c
index 03df2a7..8381e20 100644
--- a/blkparse.c
+++ b/blkparse.c
@@ -2438,14 +2438,13 @@ static int read_events(int fd, int always_block, int *fdblock)
 		struct trace *t;
 		int pdu_len, should_block, ret;
 		__u32 magic;
-
-		bit = bit_alloc();
+		void *p;
 
 		should_block = !events || always_block;
 
-		ret = read_data(fd, bit, sizeof(*bit), should_block, fdblock);
+		ret = read_data(fd, &magic, sizeof(magic), should_block,
+				fdblock);
 		if (ret) {
-			bit_free(bit);
 			if (!events && ret < 0)
 				events = ret;
 			break;
@@ -2455,15 +2454,28 @@ static int read_events(int fd, int always_block, int *fdblock)
 		 * look at first trace to check whether we need to convert
 		 * data in the future
 		 */
-		if (data_is_native == -1 && check_data_endianness(bit->magic))
+		if (data_is_native == -1 && check_data_endianness(magic))
 			break;
 
-		magic = get_magic(bit->magic);
+		magic = get_magic(magic);
 		if ((magic & 0xffffff00) != BLK_IO_TRACE_MAGIC) {
 			fprintf(stderr, "Bad magic %x\n", magic);
 			break;
 		}
 
+		bit = bit_alloc();
+		bit->magic = magic;
+		p = (void *) ((u8 *)bit + sizeof(magic));
+
+		ret = read_data(fd, p, sizeof(*bit) - sizeof(magic),
+				should_block, fdblock);
+		if (ret) {
+			bit_free(bit);
+			if (!events && ret < 0)
+				events = ret;
+			break;
+		}
+
 		pdu_len = get_pdulen(bit);
 		if (pdu_len) {
 			void *ptr = realloc(bit, sizeof(*bit) + pdu_len);
@@ -2596,20 +2608,30 @@ static int ms_prime(struct ms_stream *msp)
 	int ret, pdu_len, ndone = 0;
 
 	for (i = 0; !is_done() && pci->fd >= 0 && i < rb_batch; i++) {
-		bit = bit_alloc();
-		ret = read_data(pci->fd, bit, sizeof(*bit), 1, &pci->fdblock);
+		void *p;
+
+		ret = read_data(pci->fd, &magic, sizeof(magic), 1,
+				&pci->fdblock);
 		if (ret)
 			goto err;
 
-		if (data_is_native == -1 && check_data_endianness(bit->magic))
+		if (data_is_native == -1 && check_data_endianness(magic))
 			goto err;
 
-		magic = get_magic(bit->magic);
+		magic = get_magic(magic);
 		if ((magic & 0xffffff00) != BLK_IO_TRACE_MAGIC) {
 			fprintf(stderr, "Bad magic %x\n", magic);
 			goto err;
 
 		}
+		bit = bit_alloc();
+		bit->magic = magic;
+		p = (void *) ((u8 *)bit + sizeof(magic));
+
+		ret = read_data(pci->fd, p, sizeof(*bit) - sizeof(magic), 1,
+				&pci->fdblock);
+		if (ret)
+			goto err;
 
 		pdu_len = get_pdulen(bit);
 		if (pdu_len) {
@@ -2639,6 +2661,7 @@ static int ms_prime(struct ms_stream *msp)
 			handle_notify(bit);
 			output_binary(bit, sizeof(*bit) + bit->pdu_len);
 			bit_free(bit);
+			bit = NULL;
 
 			i -= 1;
 			continue;
@@ -2659,6 +2682,7 @@ static int ms_prime(struct ms_stream *msp)
 		}
 
 		ndone++;
+		bit = NULL;
 	}
 
 	return ndone;
-- 
2.51.0